The present invention relates in general to the supervision of the operability of transducers. More particularly, as disclosed herein, this invention pertains to the supervision of audio speakers which may be used in a loud speaker system.
There is a problem associated with audio systems and especially audio systems that are used for emergency communications. There is some difficulty in insuring that the speaker is properly connected to the audio line and in operable condition. There presently exist some techniques for supervising the operability of speakers. For example, one arrangement uses a special speaker structure which comprises a separate pick-up coil. A low (subaudible) frequency is continuously impressed on the audio lines. With this prior art arrangement the cone vibrates and the movement of the magnet within the voice coil causes an induced voltage to be generated in the secondary pick-up coil. The signal from this coil is a low level signal which may be suitably amplified and used to energize a relay or operate a gate. There are some disadvantages associated with this known system. For example, special speaker assemblies are required and existing speaker systems will require replacement of the entire speaker assembly. Also, there is a noise problem in that noise can be easily picked up by the secondary pick-up coil thereby interferring with the proper monitoring of the operability of the speaker.
Accordingly, one object of the present invention is to provide an improved technique for the supervision of transducers preferably of the vibrating type such as a loud speaker.
Another object of the present invention is to provide a supervision scheme which does not require the complete replacement of the speaker. In accordance with this invention a transducer such as a piezoelectric transducer is easily secured to the speaker for detecting sub-audio signals or low amplitude signals impressed on the audio lines.
A further object of the present invention is to provide a supervision scheme that is not susceptible to noise problems associated with prior art schemes.